A variety of medical devices for delivering a therapy and/or monitoring a physiological condition have been used clinically or proposed for clinical use in patients. Examples include medical devices that deliver therapy to and/or monitor conditions associated with the heart, muscle, nerve, brain, stomach or other organs or tissue. Some medical devices may employ electrodes for the delivery of electrical stimulation to such organs or tissues, electrodes for sensing electrical signals within the patient, which may be generated by such organs or tissue, and/or other sensors for sensing physiological parameters of a patient.
Implantable medical devices, such as cardiac pacemakers or implantable cardioverter-defibrillators, for example, provide therapeutic electrical stimulation to the heart via electrodes carried by one or more implantable leads. The electrical stimulation may include signals such as pulses or shocks for pacing, cardioversion or defibrillation. In some cases, an implantable medical device senses intrinsic depolarizations of the heart, and controls delivery of stimulation signals to the heart based on the sensed depolarizations. Upon detection of an abnormal rhythm, such as bradycardia, tachycardia or fibrillation, the implantable medical device may deliver an appropriate electrical stimulation signal or signals to restore or maintain a more normal rhythm. For example, in some cases, an implantable medical device delivers pacing pulses to the heart of the patient upon detecting tachycardia or bradycardia, and delivers cardioversion or defibrillation shocks to the heart upon detecting fibrillation.